Variable high resistance and method of making same



Nov. 2z', 1927.., A1,649,990

1 W. A. SMITH VARIABLE HIGH RESISTANCE ANDMETHOD 0F MAKING SAME vFiled Feb. 1e, 192s 2 sheets-sheet 1 Patented Nov. 22, 1921.

UNITED sTATEs PATENT OFFICE.

WALDORF A. SMITH. OF CHICAGO, ILLINOIS, ASSIGNOB TO CARTER RADIO COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION F ILLINOIS.

VARIABLE HIGH RESISTANCE AND METHOD OF MAKING Application tiled :February 18, 1926. Serial No. 89,140.

-My invention relates to variable high re sistances and method of making the saine.

It is a purpose of my invention to provide a variable resistance which may vary in value from that of the inest wire wound rheostat to substantially 100 megohms and wherein the variation follows a certain definite mathematical law or formula. More particularly it is a purpose of my 0 invention to provide a resistance element that is so made that the increase in resistance at a point at any distance from one end thereof bears a substantiall constant ratio to the total resistance of said element from said end to said point. That is, if the resistance is cut in by a movable contact means from said end, the increase in resistance as v the contact is moved along will always bear a constant ratio to the total resistance cutin. 2 This is very important as it makes it possible to increase the resistance very slowly at first and more rapidl as the total resistance is increased, so t at'the percent of regulation is the same or constant throughout the length of the resistance element.

This is accomplished by providing 4a strip of insulating material with a coating of finely divided resistance material which may be carbon particles in the case of the higher 3 resistances and articles of better conducting material, suc as finely divided or powdered metallic particles in the lower resistances, the important thing being that the coating of finely divided material serving as the resistance element is divided into two portions, one of whichis of greater conductivity than the other.

Obviously, the arrangement of the portions of resistance of higher and lower con- 40 ductivity may be varied in accordance with the character of variation desired of the resistance element along the length thereof so as to produce a rheostat having the characteristics desired. It is accordingly, a purpose of the invention to provide a resistance element having portions of diilerent conductivity whereby the conductivity along the length of said element varies as desired. In the form shown, the portion of greater conductivity begins adjacent one end of the stri and extends toward the other end thereov, decreasing in width toward the other end and terminating short of the other end, the remainder of the strip comprisingethe portion of lesser conductivity and ing substantially a complement of the portion of greater conductivity.

It .is a further purpose of the invention to provide a new and improved method of making a resistance element" comprising coating a predetermined area of a strip of insulating material with finely divided conductingmaterial of high resistance by rubbmg the same thereon, and 'subsequently coating the entire strip with a coating of adhesive material having inely divided conducting material suspended therein, thus producing a strip having a portion of greater conductivity where the first mentioned coating was first applied and a portion of lesser conductivity where only the latter coating was applied. More particularly the method comprises applyin the first mentioned coating by the rub in action over an area that decreases in wi th from one end of the strip toward the other end thereof, winding a conductor around said strip to act as a contact means for engagement by the movable contactto be used with the resistance element, severing the turns of said winding of conducting material so as to provide separate transversely extending lengths of conducting material embracing said strip, the severing means comprising rollers that form grooves in the insulating strip into which the ends of the lengths of the conducting member are forced due to the action of the rollers and then coating the stri and the conducting members thereon wit an adhesive coating that ma be made up of celluloid cr similar materia n and a finely divided or comminuted conducting material of high resistance, such as carbon suspended in said adhesive, material. This not only causes the particles of inely di- D5 vided material to be spread out over the surface of the strip substantially uniformly, but furthermore aids in holding the ends of the conducting member after the same has been severed in place, thus preventing the disengagement of the same from the stri that they embrace.

(liber objects and advantages of theinvention will appear as the description of the accom anying drawings proceeds. Howeve-r, desire to have it distinctl understood that I do not intend to limit myself to the exact details shown or described, but that I intend to include as part of my invention all such obvious changes and modifcations of parts as Awould occur to a person skilled in this art and as would fall within the scope of the claims.

In the drawings:

Fig. 1 is a view in side elevation of a variable resistance means embodying my improved resistance element.;

Fig. 2 i-s a section taken on the line 2 2 thereof;

Fig. 3 is -an enlarged fragmentary sectional view taken at right angles to Fig. 2;

Fig. 4 is a lan view of the insulating stripshowing t e first stage in the process of makin the resistance element;

Fi 5 1s a fragmentary plan viewshowing t e winding of a conducting member in place on a strip which comprises the se'cond stage in the process;

Fig. 6 is a section taken on the line 6-6 of Fig. 5;

Fig. 7 i-s a' view similar to Fig. 6 showing the strip after the next stage of the process has been carried out, wherein the conducting member is severed so as to form separate conducting members embracing the strip;

Fi 8 is a fragmentary plan view show ing t e strip after the final stage of the process has taken place; and

Fig. 9 is a section similar to Figs. 6 and 7 of the strip after the final stage of the'process has taken place.

Referring in detail to the drawings, my improved rheostat comprises an annular member 20 having a web portion 21 and a central opening 22, said web portion merging into a flange 22 which terminates in an outwardly extendino' flange 23 that is annular inform, said flange 23 it will be noted, curves or inclines toward the web portion 21 to thus provide an undercut flange portion on the periphery of the annular member 20. Cooperating with the annular member 20 is a ring-like member 24 which fits snugly over the flange 22 and which is provided with an outwardly extending fiange 25 that is inclined toward the fiange 23 so that the fianges 23, 24 and 25 form an annular groove that is undercut, as will be clear from Fig. 2.

A ring-like member of insulating material 26 is provided within the groove thus formed and the insulating rin s 27 and 28 are provided lying adjacent t ie flanges 23 and 25. Mounted within the groove is a resistance element which will be described below. A bearin member 29 is provided that extends throug the opening 22 in the web 21, said bearing member being provided with an enlargement or flanfre 30; with a portion of slightly smaller diameter 31 and with a threaded portion 32 with which the nut 33 engages to hold the parts in position. An insulating member 34 may be mounted between the flange 30 and the member 21 if desired. The member 29 is provided with an opening through which the reduced end 35 of the shaft 36 extends, the reduced end 35 being headed as indicated at 37 and a spring washer 38 being provided between the head 37 and the inner end or hub portion 39 of a contact arm 40. The contact arm 40 is provided with an arcuate portion 41 extending around and spaced from the fiange 43, a laterally extending portion 42, an inwardly extending portion 43 and a contact shoe portion 44 that engages with the resistance element forming the subject matter of the present invention.

The resistance element comprises a st rip of insulating material 45 to which a coatlng 46 of finely divided conducting material ot' preferably high resistance is applied, this being shown in Fig. 4. The coating is preferably applied by rubbing, a. piece of carbon similar to that used in a lead pencil being employed for this purpose, and a mask being placed over the uncoated portion of the strip indicated by the numeral 47 to thus 'clearly define the boundary 48 of the coating 46. The coated portion of the strip 46, it will be noted, begins atone end 49 thereof and terminates short of the other end 50 thereof, and the uncoated portion 47 is a complement, substantially, of the portion 46, the portion 46 decreasing in width from the end 49 toward the end 50 as shown in Fig. 4. After the coating 46 has been applied to the strip, a conductor in the form of a wire 51 is wound spirally around the strip from end to end thereof as s howntin Fig. 5, the same being shown more in detail in the enlarged section in Fig. 6, which also indicates the coating 46 somewhat exaggerated; The winding is then severed by cutting the turns thereof by means of a pair lof rollers or other cutting means, thus forming grooves 52 in the strip 47 into which .the tapered cut ofi` ends 53 of the wire 5l are bent due to the action of the rollers. After this has been done, the entire strip is coated along with the conducting members 51, which are now short transversely extending lengths of conductor embracing the strip 45, with an adhesive coating, such as celluloid, in which is suspended a finely divided conducting material of high resistance, such as finely divided or comminuted carbon.`

This coating adheres to the conductors 51 as well as to the strip 45, both at the previously coated and uncoated portions thereof, the coating being indicated by the numeral 54 in Figs. 8 and 9. The coating material will also adhere in the grooves formed at 52 and around the ends 53 of the conductors as indicated at 55 to thus cement the ends of the conductors in position, this being very important because the ends 53 would otherwise frequently become loosened, thus destroying the value of the resistance element. It is immaterial that the conducting members 5l are coated as the coating issoon rubbed 0E by the contact shoe 44 to thus provide a good contact between the resistance strip and the shoe. It is also immaterial that the previously coated portieri 46 is given a second coating, as the first applied coating is of greater conductivity than the second, and the relative proportions of the portions 46 and 47 along the length of the strip can be so made as to allow for any slight increase in conductivity that may occur due to the application of a double coating to this portion of the strip.

The portions 46 and 47 of the strip are preferably so shaped that as the contact shoe 44 moves from the end 49 toward the end 50, the increase in resistance is always in the same proportion to the total resistance cut in from the end 49 to the contact shoe 44 and similarly the decrease in resistance is in the same proportion when the shoe is moved in the opposite direction. This is highly desirable as a more uniform adjustment for most practical purposes can be obtained in this manner, particularly in connection with radio receiving apparatus.

The member 24 is provided with va pair of upstanding ears 56 and 57 and the insulating ring 28 is provided with similar ears 58 which align with the ears 56 and 57. The ear 56 is provided with preferably a D shaped opening 59, while the ear 58 aligning therewith is provided with a similarly shaped opening 60 which :is smaller than the opening in the ear 56. In a similar manner, the ear 57 is provided with an opening of any shape and the ear 58 -aligning therewith with a smaller opening of corresponding shape. Thus the binding screw 61 is insulated from the ear 56, the same being connected with the resistance element through a strip of good conductin material 62 which may be of copper and w ich rests against the flat side of the D shaped opening 60 and embraces the insulating strip including the conducting members 51, as indicated at 63. The other binding screw 64 has the head thereof in direct contact with the ear 57. The head 66 of the binding screw 61, however, is insulated from the ear 56 by means of the insulating washer 67, as will be clear from Fig. 2.

yHaving thus described my invention, what I desire to claim and secure by United States Letters Patent is:

1. A resistance element comprising a. strip of insulating material having high resistance material on the surface thereof, said high resistance material comprising a portion of relatively lower resistance of varying width adjacent from one. end of'said strip to a point adjacent the other end thereof and a portion of relatively higher resistance extendlng the length of said strip.

2. A resistance element comprising a strip of insulating material having high resistance material on the surface thereof, said high resistance material comprising a portion of relatively high resistance extending from adjacent one end of said strip and decreasing in width toward the other end thereof and a portion of relatively higher. resistance exten-ding the length of said strip.

3. A high resistance element comprising a strip of insulating material having a coating thereon of resistance material comprising a portion of relatively higher resistance and a portion of relatively lower resistance, the proportion of said portions varying lengthwise of saidd velement in accordance with a predetermined law, one of said portions comprising an adhesive coating overlying and protecting the other portion.

4. A resistance element comprising a strip of insulating material having a coating of finely divided high resistance material partly covering the same, spaced conducting members embracing said strip and an adhesive coating having finely divided conducting material therein on said strip and covering said high resistance material.

5. A resistance element comprising a strip of insulatin material having a coating of finely divide high resistance material partly covering thesame, spaced conducting members embracing said stri and an adhesive coating having finely ivided conducting material therein on said strip and said conducting members to secure said members to said strip.

6. A resistance element comprising a strip of insulating material having comminuted conducting material on the surface thereof, comprising. two-layers of differingconductivity, one of said layers decreasing 1n width from` one end thereof toward the other end thereof the other layer completely covering said first named layer.

7. A resistance element comprising a strip of insulating material having comminute conducting material on the surface thereof, comprising two layers of differing conductivity, one of said layers decreasing in width from one end thereof toward the other end thereof and the other of said layers surrounding said first mentioned layer and ysaid insulation strip.

8. The method of making a high resistance element comprising applying a. coating of finely divided high resistance material to a portion of a strip of insulating material, se curing a conducting member in embracmg relation to sai-d strlp, severing the same to provide unconnected spaced conducting members -on said strip and applying an a hesive coating having finely divided high resistance material therein to said strip with the conducting members thereon.

9. The method of making a high resistance element comprising applyinga coating of inely divided high resistance material of varying Width to a portion of a strip of insulating material, securing a conducting member in embracing relation to said strip, severing the same to provide unconnected spaced conducting members on said strip and applying an adhesive coating having finely divided high resistance material therein to said strip with the conducting members thereon. i

.10. The method of making a high resist- Y ance element comprising rubbing a coating of finely divided high resistance material on a portion of a strip of insulating material, securinga conducting member in embracing relation to said strip, severing the same to provide unconnected spaced conducting members 0n said strip and applying an adhesive coating having finely divided'high resistance material therein to the strip of resistance material and conducting member to secure said resistance material and conducting Vmember to said strip and provide an additional layer of con-ducting material.

11. The method ofmaking a resistance element comprising applying a coating of comminuted conducting material to a portion of a strip of insulating material, secur ing a conducting member in embracing relation to said strip, severing the same to provide unconnected spaced conducting members on said strip and applying an adhesive coating having comminuted material of different conductance than said first mentioned coating to said strip with the conducting members thereon.

In witness whereof, I hereunto subscribe my name this llthjday of February, A. D. 1926.

WALDORF A. SMITH. 

